Project Summary: Retrofitting and naturalizing a retention basin in Indiana improved water quality by filtering out sediments and pollutants from stormwater, decreasing the harmful impact of storms, and improving aquatic wildlife habitats.

Location: Valparaiso, Indiana

Summary: Retrofitting and naturalizing a retention basin in Indiana improved water quality by filtering out sediments and pollutants from stormwater, decreasing the harmful impact of storms, and improving aquatic wildlife habitats.

Prior to the retrofits, the Thorgren Basin was designed only to redirect, and not to treat, contaminated stormwater. Photo courtesy of Save the Dunes.

Description: One of the biggest threats to the Great Lakes is polluted runoff that occurs when heavy rains wash pesticides, fertilizer, sediment, animal waste, oil and other pollutants into area rivers and streams—and eventually the Great Lakes. To control stormwater flow within a local watershed, the City of Valparaiso, Ind., constructed a traditional concrete detention basin The basin itself is roughly 2 acres in area, but is responsible for collecting stormwater from approximately 330 acres, most of which are commercial, industrial, or residential. As stormwater flows over this heavily developed land, it picks up sediment and pollutants and introduces them into the detention basin. The basin was not designed to slow down water flow, and therefore did not filter sediments and pollutants out of the flowing water. The stormwater, and everything it carries, is eventually emptied into Knode Creek, from which it enters the Salt Creek watershed and eventually Lake Michigan. This sediment and nutrient loading adversely impacted the water quality of the Salt Creek watershed; parts of it have become contaminated with harmful E. coli bacteria that can cause illness in people and animals. Other aquatic habitats throughout the watershed have also become highly impaired.

Meandering channels were constructed to slow down the rate of stormwater flow, and the concrete lining was removed. Photo courtesy of Save the Dunes.

Thanks to a grant from the Great Lakes Restoration Initiative, Save the Dunes, and the City of Valparaiso have partnered to naturalize and retrofit the Thorgren Basin by removing concrete and naturalizing landscaping and vegetation in the swale. They aim to expand the basin’s functionality, having it treat stormwater and provide aquatic habitat in addition to redirecting storm flows. At each inlet to the basin, sediment traps were constructed to remove much of the sediment picked up by the stormwater. The channels were reconstructed to give them a meandering path that slows down the flow of stormwater, allowing sediments and pollutants to settle out. Crews removed the concrete lining the channels, replacing it with bio-swales of native vegetation. Crews also landscaped the basin to provide a varied topography for wildlife habitats, creating clay-lined permanent pools, transitional wetland zones, and upland infiltration areas. Native vegetation was planted throughout the basin to naturalize its hydrology.

In addition to treating and redirecting stormwater, the retrofitted basin includes a varied topography with native vegetation to provide wildlife habitat. Photo courtesy of Save the Dunes.

Primary construction on the Thorgren Basin retrofits was completed in November 2012. In addition to increasing the overall carrying capacity of the basin and therefore reducing the impact of harmful storms, this project has significantly improved water quality throughout the Salt Creek watershed. The retrofits are expected to annually prevent 402 pounds of nitrogen, 130 pounds of phosphorus, and 23 tons of sediment from entering the watershed. The project is also expected to increase oxygen levels in the water for the organisms that need it, reducing biochemical oxygen demand by 3,590 pounds annually. This project has greatly increased habitat availability and quality for aquatic wildlife communities.

Approximate cost of project: $815,000 including $607,000 provided by the Great Lakes Restoration Initiative.

Types of jobs created: Local environmental contractors, professors, and general labor.

Results and accomplishments: This project is expected to annually prevent 402 pounds of nitrogen, 130 pounds of phosphorus, 3,590 pounds of biochemical oxygen demand, and 23 tons of sediment from entering the Salt Creek watershed, which eventually flows into Lake Michigan. This has significantly improved the water quality for both the people and wildlife in the area.